Plastic sheet for a boat hull and the like and method of making it

ABSTRACT

A FRP laminate composed of synthetic resin material, which contains spheres, and short strands of chopped fibers mixed into the resin/sphere blend in criss-cross, hodge-podge fashion, the sphere members and high application pressure combining to force down any upstanding chopped fibers and to make the chopped fibers lie flat in the resin layer and to knock air out of the resin layer, said sphere members comprising a plurality of high density spheres. A method of making a FRP laminate for a boat hull or the like includes spraying into a mold a synthetic resin liquid containing spheres while simultaneously applying chopped glass fibers into the fan-shaped stream of resin/sphere blend with the chopped fibers being randomly distributed in the resin layer in a hodge-podge fashion. The inclusion of the spheres in the resin provides body to the resin itself, so that, with the higher than normal spray pressure being used, there is an impacting force exerted against the glass fibers which forces them into a horizontal, randomly aligned position, thus achieving the end result of a subsequent-to-application rolling process without the need for the rolling process. The forceful application of the resin/sphere blend and the chopped fibers is sufficient to eliminate the trapped air which occurs in normal spray applications of resin and chopped fibers. An apparatus for molding FRP laminate composed of high viscosity synthetic resin, cut fibers, and spheres includes a spray gun, a high pressure spray pump upstream of the spray gun, a fluid transfer pump upstream of said spray pump, and an accumulator between the high pressure pump and the spray gun to eliminate pulsing which otherwise occurs when the spray pump reverses the direction of its stroke, whereby the high viscosity resin is properly fed from its storage container to the spray gun and a smooth steady spray is obtained.

This is a divisional of co-pending U.S. patent application Ser. No.07/616,239 filed on Nov. 20, 1990 now U.S. Pat. No. 512,617.

FIELD OF THE INVENTION

This invention relates to a modification to the typical synthetic resinmaterials used in a spray application in its liquid form in conjunctionwith chopped strands of fiberglass or other fibrous reinforcingmaterial, which resin/fiber combination is used extensively in variousmanufacturing applications, such as, but not limited to, boat hulls,shower, tub, hot-tub, spa, and swimming pools, camper and vanassemblies, pleasure boats, building cladding panels, etc. Thisinvention also relates to a modification in the application method ofthe resin/fiber material.

DESCRIPTION OF THE PRIOR ART

Many products today are constructed of synthetic resin materialreinforced by fibers. The most common fiber used is glass fiber, such asFiberglass, and the most common synthetic resin used is a polyesterresin. Products fashioned from this combination of resin and fibers arecommonly called FRP (Fiber Reinforced Plastic) products.

The fibers may also be Kevlar man-made fibers or carbon fibers, but,because of the cost and complexity in applying these materials, they areused only in a small percentage of fiber-reinforced products. Kevlar isa registered trademark of E.I. dupont deNemours and Company, Wilmington,Delaware.

The synthetic resin material may also be an epoxy resin, a vinyl esterresin, a urethane, a urethane/polyester resin, or any other suitablesynthetic resinous material.

In many of the products constructed of the fiber-reinforced syntheticresin, both the fiber and the synthetic resin are applied to the moldused to determine the shape of the product by means of a spray of theresin in which short lengths of the fiber are imbedded.

The resin is syphoned or drawn from a storage container and fed througha pump creating high pressure through a spray gun assembly while acatalyzing agent is fed from another storage container into the streamof resin, ether just after the resin leaves the spray tip attached tothe nozzle of the gun (known in the trade as an "external mix unit"), oris fed into the stream of resin passing through the feeder hose and intoa static mixer shortly before it reaches the spray tip (known in thetrade as an "internal mix unit"). The spray tips are designed to causethe existing material to spread into a fan shape.

The short strands of fiber are generated from a multi-strand string ofthe fiber being used (most commonly, fiber-glass which is known in thetrade as "gun-roving") which is drawn from a spool of the fiber into anassembly which is attached to the spray gun, and which chops the fibersinto predetermined short lengths (suitable lengths range from 0.250" to2.000") and simultaneously blows them into the fan-shaped stream ofresin shortly after the resin leaves the spray nozzle.

The fibers in this method of application are imbedded in the resin onthe mold in a random fashion. Maximum strength of the finished part isachieved only if the fibers are thoroughly wet by the resin, and alltrapped air is removed from the part being formed. The finished partsusually require a relatively smooth inner surface, but, in the asapplied state, as a result of the random nature cf the fiber imbeddingin the resin, many fiber ends protrude from the surface, creating anunacceptable surface condition. Substantial air entrapment occurs inthis method of resin-fiber application, which must be removed.

In order to ensure maximum wet-out of the fibers, removal of trappedair, and creation of a relatively smooth inner surface, common practiceis to roll the resin-fiber layer while the resin is still in an uncured,liquid state. Because of the complexity of the shape of most products,this rolling procedure is normally done manually, adding a highlylabor-intensive step to the manufacturing process of the product beingformed, and providing for the possibility of uneven or poor quality ofthe finished product.

It has long been the desire of users of the resin-chopped fiber sprayapplication method to be able to eliminate this labor-intensive rollingstep from their production process. This invention accomplishes this formany such users.

SUMMARY OF THE INVENTION

In products or parts formed from synthetic resin material reinforced byshort lengths of fiber which are applied to the product or partsimultaneously with the resin in a spray application, it is an object ofthis invention to eliminate the labor-intensive roll-out step in themanufacturing process.

It is another object of this invention to ensure a more consistentquality in such products or parts.

It is another object of this invention to reduce the time required tofinish such products or parts, thereby allowing more uses of the mold ina given time.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic view of the apparatus for molding sheets ofhigh viscosity synthetic resin, cut fibers, and spheres, in accordancewith the invention.

DESCRIPTION OF THE INVENTION

It has been found that if prior to the application of the syntheticresin material to the mold, the resin has had blended into it a highpercentage by volume of relatively high density microspheres or otherhigh density, bulky fillers, all of a sufficiently large diameter(hereinafter referred to as "spheres"), composed of glass, mineral,aluminum silicate, or other materials, and that if this blend of resinand spheres is sprayed at higher spray pressures (such as 400 psi to2000 psi) than normally used (180 psi to 360 psi) in the application ofchopped fibers and resin via spray, the resulting impact forcesgenerated by the spheres upon the chopped fibers causes the fibers toform into a non-uniform but horizontally oriented position, with few ifany fiber ends protruding from the surface. The high spray pressure andthe sphere bombardment also effectively eliminate any trapped air, andserve also to aid in the thorough wetting of the short fibers ofreinforcing material.

Thus, by the inclusion of particles with suitable body and density inthe resin being sprayed, coupled with equipment modifications to permitmore than normal application pressure of the highly viscous resin-sphereblends, it becomes possible to eliminate the labor intensivehand-rolling process normally required when applying resin-chopped fibersimultaneously by the spray method, while producing a more consistentproduct quality-wise. This presents a significant improvement in anapplication process that has been in extensive use in many industriesfor over forty-five years.

The method of making a FRP laminate for a boat hull or the like,comprises the steps of spraying a synthetic resin liquid into a mold toform a layer of resin, simultaneously applying chopped glass fibers tothe mold with the chopped fibers being randomly distributed in the resinlayer in a hodge-podge fashion with some fibers standing up in the resinlayer and extending outside the resin layer, and spraying heavy spheresonto the resin layer to knock down any upstanding fibers to make themlie flat in the resin layer and to knock air out of the resin layer.

The spheres comprise 30% to 60% by volume of the sheet, and the specificgravity of the spheres is greater than 0.025. The spheres are 30 to 600microns in diameter, and they may be composed of mineral, glass,aluminum silicate, or other high density, bulky fillers.

The chopped fibers are preferably made of glass and are known as glassfibers.

The presently preferred spheres are SCOTCHLITE glass bubbles as sold by3M, St. Paul, Minnesota. SCOTCHLITE glass bubbles have as an ingredientsoda lime borosilicate glass (amorphous silicate), and a particularlypreferred bubble type is B37/2000.

The blend of resin and spheres has a viscosity too high to allow properfeeding from its storage container 19 when using standard resin sprayequipment. It was found that adequate, continuous flow of the blendcould be had by the addition of a fluid transfer pump 15 (such as abellows pump) to the feed line prior to the high pressure spray pump 13.Other methods of delivering material in an adequate, continuous flow tothe high pressure pump can be used, such as a follower plate (plunger)used to force material out of a drum up through a tube in the center ofthe follower plate. It also was found to be necessary to add anaccumulator 17 between the high pressure pump 13 and the spray gun 11 toeliminate pulsing which otherwise occurs when the high pressure pump 13reverses the direction of its stroke. Without these equipmentmodifications, a smooth, steady spray does not occur.

In the resin-sphere blend application equipment, a fluid transfer pump15 has been incorporated into the standard resin spraying equipmentprior to the high pressure pump 13 so as to be able to withdraw theviscous resin-sphere blend from its storage container 19 and deliver itin a satisfactory continuous stream to the high pressure pump 13 used togenerate the high spray pressure needed to deliver a commerciallyacceptable volume of the resin-sphere blend through standard spraynozzles.

Also, an oversized accumulating chamber 17 has been added between thehigh pressure pump 13 and the spray gun 11 to reduce the pulsing actionotherwise caused by the time lag occurring by the reversal of thedirection of the high pressure pump piston. I claim: 1. A FRP laminatecomprising

a layer of synthetic resin material,

short strands of chopped fibers mixed into the resin in criss-cross,hodge-podge fashion, and

sphere means mixed into the chopped fibers and the resin to force downany upstanding chopped fibers and to make the chopped fibers lie flat inthe resin layer and to force air out of the resin layer,

said sphere means comprising a plurality of high density spheres. 2. TheFRP laminate of claim 1, said spheres comprising 30% to 60% by volume ofthe sheet. 3. The FRP laminate of claim 1,

the specific gravity of the spheres being greater than 0.025. 4. The FRPlaminate of claim 1, the spheres being 30 to 600 microns in diameter. 5.The FRP laminate of claim 1,

the spheres being composed of mineral, glass, aluminum silicate, orother high density, bulky fillers. 6. The FRP laminate of claim 1,

the chopped fibers being made of glass. 7. A FRP laminate comprising,

a layer of synthetic resin material,

short strands of chopped fibers mixed into the resin in criss-cross,hodge-podge fashion, and

sphere means mixed into the chopped fibers and the resin to force downany upstanding chopped fibers and to make the chopped fibers lie flat inthe resin layer and to force air out of the resin layer,

said sphere means comprising a plurality of hiqh density spheres,

said spheres comprising 30% to 60% by volume of the sheet,

the specific gravity of the spheres being greater than 0.025,

the spheres being 30 to 600 microns in diameter,

the spheres being composed of mineral, glass, or aluminum silicate, and

the chopped fibers being made of glass.

I claim:
 1. A FRP laminate comprisinga layer of synthetic resinmaterial, short strands of chopped fibers mixed into the resin incriss-cross, hodge-podge fashion, and sphere means mixed into thechopped fibers and the resin to force down any upstanding chopped fibersand to make the chopped fibers lie flat in the resin layer and to forceair out of the resin layer, said sphere means comprising a plurality ofhigh density spheres.
 2. The FRP laminate of claim 1, said spherescomprising 30% to 60% by volume of the sheet.
 3. The FRP laminate ofclaim 1,the specific gravity of the spheres being greater than 0.025. 4.The FRP laminate of claim 1, the spheres being 30 to 600 microns indiameter.
 5. The FRP laminate of claim 1,the spheres being composed ofmineral, glass, aluminum silicate, or other high density, bulky fillers.6. The FRP laminate of claim 1,the chopped fibers being made of glass.7. A FRP laminate comprising,a layer of synthetic resin material, shortstrands of chopped fibers mixed into the resin in criss-cross,hodge-podge fashion, and sphere means mixed into the chopped fibers andthe resin to force down any upstanding chopped fibers and to make thechopped fibers lie flat in the resin layer and to force air out of theresin layer, said sphere means comprising a plurality of hiqh densityspheres, said spheres comprising 30% to 60% by volume of the sheet, thespecific gravity of the spheres being greater than 0.025, the spheresbeing 30 to 600 microns in diameter, the spheres being composed ofmineral, glass, or aluminum silicate, and the chopped fibers being madeof glass.